Method of inhibiting corrosion of ferrous metals



United States Patent 3,258,424 METHOD OF INHKBITING CORRUSION 0F FERROUSMETALS Edwin E. Claytor, Jr., Tulsa, Okla, assignor to Pan AmericanPetroleum Corporation, Tulsa, ()klzn, a corporation of Delaware NoDrawing. Filed Aug. 2, 1963, Ser. No. 299,454

12 Claims. (Cl. 252-855) This invention relates to inhibiting corrosion.More particularly, it relates to inhibiting the corrosion of ferrousmetal surfaces by the oil-field corrosive materials hydrogen sulfide,low molecular weight organic acids such as acetic and propionic acids,carbon dioxide, oxygen, and combinations of these corrosive materials.

In US. Patent 2,756,211, Jones, the use of salts of high molecularweight primary amines, and high molecular weight carboxylic acids toinhibit oil-field corrosion is disclosed and claimed. Certainembodiments of these salts have now been in successful widespread usefor many years. The most common treating procedure has been to contactthe metal surfaces first with a high concentration of the amine salt toform a protective adsorbed film, and then make periodiclow-concentration treatments to keep the film in repair.

As more field operations have been made automatic, the frequency of apumper visiting a well has decreased. The frequency of intermittenttreatment with corrosion inhibitors has correspondingly decreased. Thishas placed a greater emphasis on the need for inhibitors with long filmlives. The problem is, of course, particularly severe where high flowrates or similar conditions exist for agitating the corrosive liquidsand thus removing the film more quickly. High temperatures have alsotended to remove the films rapidly, thus requiring frequent intermittenttreatments to keep the fihns in repair. An extreme case, for example, isin deep, high-temperature wells along the Gulf of Mexico coast whereboth flow velocities and temperatures are'frequently high at the bottomof a well. Most of these Wells are flowing wells which require littleattention except for the introduction of corrosion inhibitors.

An object of this invetnion is to provide a method for inhibitingcorrosion which produces longer lasting protective films and thusrequires less frequent treatment with film-forming inhibitors. Stillother objects will be apparent from the following description andclaims.

In general, I accomplish the objects of my invention by the use, asinhibitors, of amine salts and amides of a particular acid andderivatives of the acid. The acid is 4,4-bis(4 hydroxyphenyl) pentanoicacid. A more common name is Diphenolic Acid. Although this term and theabbreviation DPA are both trademarks, they are used hereinafter forconvenience and mean herein only the compound the structure of which isas follows COOH This can be simplified to H0((J H1 )0H COOH 3,258,424Patented June 28, 1966 The amides are, in general,

stnaight chain fatty acids. better than the amine salts.

The explanation of the superior action'of the amides and amine salts ofDiphenolic Acid and its derivatives is not completely certain, butappears to lie in the peculiar nonemulsifying structure of the acidmolecule. It has been known for some time that an amine salt, or amide,which has emulsion-forming tendencies, is not as good an inhibitor as anapparently equivalent salt or amide without emulsion-forming tendencies.The Diphenolic Acid, both because of its nonlinear structure and polargroups in addition to the acid radical, has less emulsifyingcharacteristics than the straight chain soapm aking acids.

The amine can be any of the many high molecular weight amines havingmore than about 10 carbon atoms per molecule listed in such referencesas US. Patents 2,756,211, Jones, 2,736,658, Pfohl et -a1., 2,914,557,Oxford, 2,598,213 Blair and the like. The amines which now seem to 'bepreferred in the industry are those having the formulas RNH(CH2)2NH(CHz)2NH2 where R is an aliphatic hydrocarbon radical havingabout 16 to 18 carbon atoms.

These polyamines are particularly useful with some of the preferredDiphenolic Acid derivatives. The preferred acid derivatives are those inwhich at least two carboxylic acid groups occur in the same molecule.The polyam-ine and the polyacid can react to form a high molecularweight cross-linked salt or amide. The linkages are not, in general, asstrong as those in cross-linked plastics, for example, but are strongenough to add to the apparent molecular weight and film stability of thesalts and amides.

Some examples of polybasic Diphenolic Acid derivatives which have beenfound satisfactory, together with shortened names, are as follows:

For convenience, these derivatives will be referred to hereinafter bytheir simplified names. In these names DPA, of course, stands forDiphenolic Acid, which is, itself, a simplified name.

The dimer diester DPA was formed by reacting 2 mols of DPA with 1 mol ofa mixture of dimer acids having the average formula C H (COOH) The dimeracid linked 2 DPA molecules together through phenolic linkages so theresulting molecule had two carboxylic acid groups.

To demonstrate the film stability of the amine salts and amides ofDiphenolic Acid and its derivatives, two

principal types of tests were made. One was a flow test while the otherwas the so-called wheel test.

In the flow test, thin strips of mild steel were exposed to thecorrosive liquids, the rate of corrosion being measured by recording thechange of electrical resistance of the strips. After an initial rate ofcorrosion was established, the strips were immersed in a solution of thecorrosion-inhibiting composition. The corrosion-inhibiting solution wasthen allowed to drain off the strips. The strips with their films ofinhibitor were then again exposed to the flowing stream of corrosiveliquids. A decreased rate of corrosion was noted until the film waslost. When the film was lost, the corrosion rate returned to theoriginal value. The time required for the corrosion rate to return tothe original value was, therefore, a measure of the film life of thecorrosion inhibitor. The testing apparatus and method are described inmore detail in an article entitled, Laboratory Flow Test for Evaluationof Oil Well Corrosion Inhibitors, in the periodical, Corrosion, forAugust 1962, page 227t.

Results of flow tests at a room temperature of about 75 to 80 F. arereported in Table I. In these tests the concentration of inhibitor inthe inhibiting solution was 25,000 parts per million (2.5 percent). Thecorrosive liquids were a 50-50 mixture of oil and water. The oilconsisted of hydrocarbons containing from about 10 to 12 carbon atomsper molecule. The water was a percent sodium chloride brine containingabout 700 parts per million of hydrogen sulfide. The flow rate ofcorrosive liquids was about 1 foot per second. The pH of the brine phasewas about 5.7.

The amine portion of both the amides and salts was the same in all casesin Table I to permit better comparison of the various acids. The aminewas a mixture of polyamines having the formula RNH(CH NH R beinganaliphatic hydrocarbon radical having usually 16 to 18 carbon atoms. Eventhough the amine was a polyamine in every case, enough amine was used toprovide one amine molecule for each carboxylic acid radical. Thus, intribasic DPA three moles of amine per mole of the acid derivative wereused since each acid molecule contained three carboxylic acid groups.

The DPA soya .monoester salt result is included since it illustrates twopoints. First, it shows that a long aliphatic hydrocarbon radicalattached through an ester linkage to the Diphenolic Acid gives that acidenough emulsifying characteristics to produce a short film life. Second,the test shows, in a rather extreme form, the short film life typical ofthe soap-forming acids. Many of the soapforming acids provide a somewhatbetter film life than in Test 7 of Table I, but the results aresometimes erratic. Test 4, using the dimer diester, shows that, if bothends of the long hydrocarbon radical can be attached to Diphenolic Acidmolecules, the results are quite good. In order for the emulsifyingtendency to be serious, it will be apparent that the Diphenolic Acidderivative must have a free-end aliphatic hydrocarbon radical longenough to cause emulsifying tendencies. Ordinarily, the hydrocarbonradical must contain at least about 12 carbon atoms to provideemulsifying properties. Stated in another way, this means that in orderfor the Diphenolic Acid derivatives to be suitable for my purpose, theymust have no free-end aliphatic hydrocarbon radical containing more thanabout 12 carbon atoms.

The test of polyglycidyl DPA and amine is included in Table I since theepoxy resin formed in this Way has been found to be an excellentinhibitor for high-temperature acid corrosion. This use is described inmore detail, and is claimed, in my co-pending patent application S.N.299,464, filed August 2, 1963. The inhibitor in this case was formed byreacting one mole of Diphenolic Acid with three moles of epichlorohydrinand then attempting to cross-link the resin by adding the same polyamineused to form the salts and amides. Test 9, using this resin film, showsthat simply increasing the molecular weight of the acid bypolymerization with epichlorohydrin or the addition of a polyamine atlow temperature does not provide the degree of corrosion inhibition northe film life provided by the Diphenolic Acid derivatives which can formamine salts or amides. The principal reason is probably failure of theamine to react at the low temperature. Tests 1 to 6, and 8, show thevery good results provided by the amine salts and amides. It should bementioned that the flow test is severe. Therefore, the film life of only50 or 60 hours in the test indicates a better film life than can beexpected from many inhibitors now used commercially.

The second type of test, the wheel test, has been in use in many testinglaboratories for several years. There have been a number of variationsof this test. The one most widely used seems to be a version in whichcoupons of mild steel are weighed and then soaked in a concentratedcorrosion inhibitor solution to form a film of the inhibitor. The couponis then placed in a bottle containing corrosive liquids. This bottle isplaced at or near the outer edge of a wheel on a horizontal axle. TheWheel is turned several times a minute. This turns the bottle overseveral times a minute to provide agitation of the corrosive liquids incontact with the treated surfaces of the metal coupons. After thedesired period of treatment, the coupons are cleaned and again weighed.Percent inhibition is calculated by comparison to the weight lost from acoupon treated with oil containing no inhibitor.

Table II presents the results of wheel tests in which two differentstrengths of inhibitor were used. The corrosive liquids were actualfield-produced fluids from a well. The fluids contained no hydrogensulfide, but did contain carbon dioxide and low molecular weight organicacids. The fluids were 36 percent oil and 64 percent water.

TABLE II Percent Inhibition Test Inhibitor At 2,500 At 15,000 ppm.p.p.m.

DPA monoamide 79 DPA salt 69 71 Tribasic DPA salt 62 71 'Ietrabasic DPAsalt 82 81 Dimer diester DPA salt 81 81 Dimer diester DPA amide 78 77The amine used, and the ratio of amine to acid, in every case was thesame as described in connection with Table I. The Diphenolic Acid saltemployed twice as much amine as acid on a molecular basis. This ratiowas used in an effort to cause the amine to associate with the phenolicgroups as well as reacting with the carboxylic acid group of theDiphenolic Acid. It will be apparent from the results reported in thetable that all the materials tested were good inhibitors for this typeof corrosion. The Diphenolic Acid salt and the tribasic DPA salt seemeda little less desirable than the other materials, but films of eventhese salts in a concentration above about 2,000 parts per millionprovided considerable inhibition in the presence of agitated corrosiveliquids.

- One of the most widely used of the amine salt inhibitors at thepresent time is the salt of naphthenic acid with the amine used informing the salts and amides listed in the tables. The naphthenic acidsalt was not tested with the particular corrosive well fluids used inthe tests reported in Table II. With similar fluids, however, thenaphthenates have provided, on the average, about 20 to 30 percentprotection in wheel tests. Wheel tests of naphthenates in some wellfluids show about the same degree. of protection. The naphthenatesprovide excellent inhibition in the field where frequent treatment ispossible. It will be apparent that the Diphenolic Acid derivativesprovide better films than the naphthenates and are, therefore, to beconsidered superior, particularly where treatments are less frequent.

7 To check the ability of the inhibitor films to inhibit oxygencorrosion, mild steel coupons were dipped in inhibitor solution,drained, baked at 160 to 180 F. for two hours to insure completion ofany reactions, and then exposed for 24 hours to a salt water spray inthe presence of atmospheric oxygen and a temperature of 95 to 100 F.Results of the tests are reported in Table III.

TABLE III Inhibitor Inhibition,

percent DPA monoamide Tribasie DPA amide Tetrabasic DPA amide Dimerdiester DPA amide Tetrabasie DPA salt DPA soya monoester salt Dimerdiester DPA salt Polyglycidyl DPA amine All the materials listed inTable III have been previously identified in connection with Table I.The inhibitor solution in which the coupons were dipped contained 25percent of the inhibiting compounds. It will be apparent from the datain Table III that the amides and salts of Diphenolic Acid and itsderivatives are effective to inhibit oxygen corrosion. Some are betterthan others. In Test 6 it will be noted that the emulsion-formingtendency of the soya monoester was not a disadvantage in the spray test,possibly because of the absence of oil in the test. The epoxy resin saltformed in Test 8 was obviously highly effective against oxygen corrosioneven though it was not effective in the presence of hydrogen sulfide asshown in Table I. The high temperatures used in the baking step of theprocedure of the tests reported in Table III were apparently able tocause the amine to react with the polyglycidyl DPA and form an effectiveepoxy resin coating on the metal surface. In the tests of Table I thetemperatures seem to have been too low to permit the polymerizationreactions to occur. The baking step had little effect on the amides, ofcourse, but tended to convert the amine salts to the amides.

It will be apparent from the data in the tables that amides and aminesalts of Diphenolic Acid and may of its derivatives are highly effectivein forming long-lasting films which inhibit corrosion by hydrogensulfide, oxygen, carbon dioxide, low molecular weight organic acids, andmixtures of these agents. The derivatives should be limited to thosehaving no free-end hydrocarbon radicals containing more than about 10carbon atoms. The group should include, in addition to the compoundsnamed in the tables, others such as the polyether acids identifiedabove. No film life tests are available for these derivatives, butstatic bottle tests show the polymers to be good inhibitors and theirsimilarity to the derivatives reported in the tables would certainlyindicate that films of the polyether acid derivatives are alsolong-lasting.

The Diphenolic Acid inhibitors are principally appli cable to thosemethods of corrosion inhibiting in which the metal surface to beprotected is exposed to a solution containing a high concentration ofthe inhibiting compound in order to form a good film and is then exposedto the corrosive fluids. Thus, use in so-called squeeze treatments orslug treatments in wells is advantageous since in both cases a ratherlarge volume of high-concentration inhibitor solution is introduced intothe well to coat exposed metal surfaces, no further treatment then beingprovided for a long period of time. It will be apparent, however, thatthe salts and amides are also useful in methods in which smaller amountsof inhibitor in lower-concentration solutions are introduced morefrequently into a well, for example. The inhibitors are not limited inusefulness to oil wells, but may also be used in flow lines, tanks andthe like, in oil fields. In addition, the inhibitors may be used inrefineries or chemical manufacturing plants where corrosion from thevarious types of corrosive agents named above may be a problem.

I claim:

1. A method for depositing a long-lasting film for inhibiting corrosionof a ferrous metal surface by an aqueous solution of a corrosive agentselected from the group consisting of hydrogen sulfide, carbon dioxide,low molecular weight caboxylic acids and combinations of these agents,said method comprising contacting said surfaces with a salt of an aminehaving an aliphatic hydrocarbon radical containing at least about 10carbon atoms and an acid selected from the group consisting of 4,4-bis(4-hydroxy phenyl) pentanoic acid; 4,4-b'is (4-carboxyrnethyl phenyl)pentanoic acid and di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenylester of a dimer acid having the approximate formula C H (COOH) and thenexposing said surface to said solution of corrosive agent.

2. The method of claim 1 in which said surface is contacted with asolution of said salt containing at least about 2,000 parts per millionby weight of said salt.

3. The method of claim 1 in which said reaction product is the salt of4,4-bis(4-hyd.roxy phenyl) pentanoic acid.

4. The method of claim 3 in which the amine portion of said salt has theformula RNH(CH NH where R is a hydrocarbon radical containing from about16 to about 18 carbon atoms.

5. A method for depositing a long-lasting film for inhibiting corrosionof a ferrous metal surface by an aqueous solution of a corrosive agentselected from the group consisting of hydrogen sulfide, carbon dioxide,low 'molecular weight carboxylic acids and combinations of these agents,said method comprising introducing into said solution a salt of an aminehaving an aliphatic hydrocarbon radical containing at least about 10carbon atoms and an acid selected from the group consisting of 4,4-bis(4-hyd-roxy phenyl) pentanoic acid; 4,4-bis (4-carboxymethyl phenyl)pentanoic acid and di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenylester of a dimer acid having the approximate formula C H (COOH) 6. Amethod for depositing a long-lasting film for inhibiting corrosion of aferrous metal surface by an aqueous solution of a corrosive agentselected from the group consisting of hydrogen sulfide, carbon dioxide,low molecular weight carboxylic acids and combination-s of these agents,said method comprising contacting said surface with a salt of apolyamine having an aliphatic hydrocarbon radical containing at leastabout 10 carbon atoms and a polybasic acid derivative of 4,4-bis(4-hydroxy phenyl) pentanoic acid, said derivative being selected fromthe group consisting of 4,4-bis (4-carboxymethyl phenyl) pentanoic acid,and di 4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of adimer acid having the approximate formula C H (COOH) and then exposingsaid surface to said solution of corrosive agent.

7. The method of claim 6 in which said derivative is 4,4-bis(4-carboxymethyl phenyl) pentanoic acid.

8. The method of claim 6 in which said derivative is di4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acidhaving the approximate formula 9. The method of claim 6 in which saidpolyamine has the formula RNH(CH NH where R is a hydrocarbon radicalcontaining from about 16 to about 18 carbon atoms.

10. The method of claim 9 in which said derivative is 4,4-bis(4-carboxymethyl phenyl) pentanoic acid.

11. The method of claim 9 in which said derivative is di4-(4-(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acidhaving the approximate formula 12. A method for depositing along-lasting film for inhibiting corrosion of a ferrous metal surface byan aqueous solution of a corrosive agent selected. from the groupconsisting of hydrogen sulfide, carbon dioxide, low molecular weightcarboxylic acids and combinations of these agents, said methodcomprising introducing into said solution a salt of a polyamine havingan aliphatic hydrocarbon radical containing at least about 10 carbonatoms and a polybasic acid deravative of 4,4-'bis (4-hydroxy 20 phenyl)pentanoic acid, said derivative being selected 8 from the groupconsisting of 4,4-bis (4-carboxymethyl phenyl) pentanoic acid, and di4-(4(4-(4-hydroxy) phenyl) pentanoic acid) phenyl ester of a dimer acidhaving the approximate formula C H (COOH) References ited by theExaminer UNITED STATES PATENTS 2,598,213 5/1952 Blair.

2,756,211 7/1956 Jones.

2,893,968 7/ 1959 Greenlee 260559 X 2,920,040 1/1960 Jolly.

2,933,520 4/1960 Bader.

3,031,402 4/1962 Nelson 25251.5 3,061,553 10/1962 Riggs 252392 3,190,7346/1965 Nelson 252392 X ALBERT T. MEYERS, Primary Examiner.

JULIUS GREENWALD, Examiner.

H. B. GUYNN, Assistant Examiner.

1. A METHOD FOR DEPOSITING A LONG-LASTING FILM FOR INHIBITING CORROSIONOF A FERROUS METAL SURFACE BY AN AQUEOUS SOLUTION OF A CORROSIVE AGENTSELECTED FROM THE GROUP CONSISTING OF HYDROGEN SULFIDE, CARBON DIOXIDE,LOW MOLECULAR WEIGHT CARBOXYLIC ACIDS AND COMBINATIONS OF THESE AGENTS,SAID METHOD COMPRISING CONTACING SAID SURFACES WITH A SALT OF AN AMINEHAVING AN ALIPHATIC HYDROCARBON RADICAL CONTAINING AT LEAST ABOUT 10CARBON ATOMS AND AN ACID SELECTED FROM THE GROUP CONSISTING OF 4,4-BIS(4-HYDROXY PHENYL) PENTANOIC ACID; 4,4-BIS (4-CARBOXYMETHYL PHENYL)PENTANOIC ACID AND DI4-(4-(4-(4-HYDROXY) PHENYL) PENTANOIC ACID) PHENYLESTER OF A DIMER ACID HAVING THE APPROXIMATE FORMULA C32H62(COOH)2, ANDTHEN EXPOSING SAID SURFACE TO SAID SOLUTION OF CORROSIVE AGENT.